@jupiter_rowland That's correct, however, I was talking about user-level skinning and theming, not ones that rely on the admin to install before a user can use it.
Unless of course Friendica and Hubzilla later added user-level skinning and theming after I shut down my respective instances; or I just didn't notice it since I'm an admin of my own instances (and have access to all the settings). 😅😅
Example, Mastodon. There is a skin feature for it, but it's admin-level. Users can't skin it themselves. Misskey and forks have user-level skinning, though not well-documented.